The dynamic range of a photograph may be thought of as the range of intensity levels which may be represented in the photograph. For example, in the case of a widely used image format such as jpeg there are 8 bits per pixel which enables one of up to 256 different intensity levels to be stored at each pixel. This range is typically insufficient to represent the dynamic range that occurs in many environments. For example, where a photograph is taken of a scene of a window from inside a room or where a photograph is taken of a landscape. When a photograph is displayed on a display screen a similar limitation of dynamic range is experienced. Many displays are able to represent up to 8 bits per pixel only.
Existing approaches to increasing the dynamic range of photographs and digital images involve computing a radiance map where each pixel is represented using more than 8 bits per pixel. This typically involves taking several shots of the same scene using a tripod to support the camera and ensure it remains in the same position. This is relatively complex and time consuming and requires knowledge of the exposure settings at which images are captured. The radiance map is typically converted to a tone map to enable practical storage and/or display on apparatus configured for a maximum of 8 bits per pixel. The conversion from the radiance map to a tone map may comprise a non-linear mapping.
The embodiments described below are not limited to implementations which solve any or all of the disadvantages of known systems for computing high dynamic range photographs.